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Biomedical subjects

R Rozen

Publications and source records attributed to R Rozen.

At least 73 records · Page 4Linked to original sources
PubMed1996

Human methionine synthase: cDNA cloning and identification of mutations in patients of the cblG complementation group of folate/cobalamin disorders.

Methionine synthase catalyzes the remethylation of homocysteine to methionine in a methylcobalamin-dependent reaction. We used specific regions of homology within the methionine synthase sequences of several lower organisms to clone a human methionine synthase cDNA by a combination of RT-PCR and inverse PCR. The enzyme is 1265 amino acids in length and contains the seven residue structure-based sequence fingerprint identified for cobalamin-containing enzymes. The gene was localized to chromosome 1q43 by the FISH technique. We have identified one missense mutation and a 3 bp deletion in patients of the cblG complementation group of inherited homocysteine/folate disorders by SSCP and sequence analysis, as well as an amino acid substitution present in high frequency in the general population. We discuss the possibility that a mild deficiency of methionine synthase activity could be associated with mild hyperhomocysteinemia, a risk factor for cardiovascular disease and possibly neural tube defects.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed1996

Molecular genetic analysis in mild hyperhomocysteinemia: a common mutation in the methylenetetrahydrofolate reductase gene is a genetic risk factor for cardiovascular disease.

Mild hyperhomocysteinemia is an established risk factor for cardiovascular disease. Genetic aberrations in the cystathionine beta-synthase (CBS) and methylenetetrahydrofolate reductase (MTHFR) genes may account for reduced enzyme activities and elevated plasma homocysteine levels. In 15 unrelated Dutch patients with homozygous CBS deficiency, we observed the 833T-->C (I278T) mutation in 50% of the alleles. Very recently, we identified a common mutation (677C-->T; A-->V) in the MTHFR gene, which, in homozygous state, is responsible for the thermolabile phenotype and which is associated with decreased specific MTHRF activity and elevated homocysteine levels. We screened 60 cardiovascular patients and 111 controls for these two mutations, to determine whether these mutations are risk factors for premature cardiovascular disease. Heterozygosity for the 833T-->C mutation in the CBS gene was observed in one individual of the control group but was absent in patients with premature cardiovascular disease. Homozygosity for the 677C-->T mutation in the MTHFR gene was found in (15%) of 60 cardiovascular patients and in only 6 (approximately 5%) of 111 control individuals (odds ratio 3.1 [95% confidence interval 1.0-9.2]). Because of both the high prevalence of the 833T-->C mutation among homozygotes for CBS deficiency and its absence in 60 cardiovascular patients, we may conclude that heterozygosity for CBS deficiency does not appear to be involved in premature cardiovascular disease. However, a frequent homozygous mutation in the MTHFR gene is associated with a threefold increase in risk for premature cardiovascular disease.

Alleles↗
PubMed1996

Molecular genetic aspects of hyperhomocysteinemia and its relation to folic acid.

In a review of research by the author and her colleagues, the genetic basis of hyperhomocysteinemia and the relation between this condition and plasma folate levels are elucidated. There has recently been renewed interest in homocysteine metabolism because hyperhomocysteinemia has been associated with occlusive arterial disease and neural tube defects. The article focuses on a critical enzyme of folate metabolism, 5,10-methylenetetrahydrofolate reductase. A deficiency of this enzyme results in hyperhomocysteinemia and a wide variety of neurologic and vascular symptoms. Molecular genetic analysis of the enzyme has led to the identification of nine rare mutations associated with a severe-deficiency phenotype as well as one common mutation (found in 35% to 40% of alleles in the general population) that is proposed as a risk factor in some forms of cardiovascular disease and in neural tube defects.

Amino Acid Sequence↗
PubMed1996

Severe and mild mutations in cis for the methylenetetrahydrofolate reductase (MTHFR) gene, and description of five novel mutations in MTHFR.

Methylenetetrahydrofolate reductase (MTHFR) catalyzes the synthesis of 5-methyltetrahydrofolate, a methyl donor in the conversion of homocysteine to methionine. Patients with severe MTHFR deficiency have hyperhomocysteinemia, hypomethioninemia, and a range of neurological and vascular findings with a variable age at onset. We have previously described nine mutations in patients with severe MTHFR deficiency. A mild form of MTHFR deficiency, associated with a thermolabile enzyme, has been proposed as a genetic risk factor for cardiovascular disease and for neural tube defects. We have shown that a common missense mutation (an alanine-to-valine substitution) encodes this thermolabile variant. We now report an additional five mutations causing severe MTHFR deficiency and an analysis of genotype (alanine/valine status) and enzyme thermolability in 22 patients with this inborn error of metabolism. Six of these patients have four mutations in the MTHFR gene-two rare mutations causing severe deficiency and two mutations for the common alanine-to-valine mutation that results in thermolability. Even in severe MTHFR deficiency, the thermolabile variant is frequently observed, and there is a strong relationship between the presence of this variant and increased enzyme thermolability.

Adolescent↗
PubMed1995

Mutated methylenetetrahydrofolate reductase as a risk factor for spina bifida.

Periconceptional folate supplementation reduces the risk of neural-tube defects. We studied the frequency of the 677C-->T mutation in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene in 55 patients with spina bifida and parents of such patients (70 mothers, 60 fathers). 5% of 207 controls were homozygous for the 677C-->T mutation compared with 16% of mothers, 10% of fathers, and 13% of patients. The mutation was associated with decreased MTHFR activity, low plasma folate, and high plasma homocysteine and red-cell folate concentrations. The 677C-->T mutation should be regarded as a genetic risk factor for spina bifida.

Adult↗
PubMed1995

L206W mutation of the cystic fibrosis gene, relatively frequent in French Canadians, is associated with atypical presentations of cystic fibrosis.

Cystic fibrosis is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Over 400 mutations have been reported at this locus. Although severe forms of cystic fibrosis are usually associated with pancreatic insufficiency, pulmonary dysfunction, and elevated sweat chloride, there is a wide range of phenotypes, including congenital absence of the vas deferens, observed with some of the milder mutations. The L206W mutation, which was first identified in patients from South France, is relatively frequent in French Canadians from Quebec. In this report, we document the atypical form of cystic fibrosis associated with this mutation, in a cohort of 7 French Canadian probands.

Adult↗
PubMed1995

Localization of short/branched chain acyl-CoA dehydrogenase (ACADSB) to human chromosome 10.

Short/branched chain acyl-CoA dehydrogenase, SBCAD (gene symbol ACADSB), is a member of the acyl-CoA dehydrogenase family of genes with activity toward the short/branched chain acyl-CoA derivatives as well as short/straight chain acyl-CoAs. Southern blot analysis of DNA from a panel of human/rodent somatic cell hybrids localized ACADSB to human chromosome 10, and fluorescence in situ hybridization experiments confirmed the chromosomal assignment and refined the subchromosomal localization to 10q25-q26.

Acyl-CoA Dehydrogenase↗
PubMed1995

Effect of a covert fat dilution on the spontaneous food intake by lean and obese subjects.

Nine lean and nine obese subjects participated in two laboratory studies comparing the effects of a traditional high-fat dish (2.42 MJ and 49% as fat) and its convert fat-reduced version (1.53 MJ and 23% as fat) on subsequent food intake. Each version was consumed at the beginning of a free-choice lunch (experiment 1) or alone at lunch time (experiment 2). All subjects experienced both experiments. Three and 7 h after lunch, subjects were free to consume any of the items available in a vending machine. Food intake was measured directly. In experiment 1, by 8 h after lunch, mean cumulative energy intake (test dish included) was not different between the test dish conditions in both lean and obese subjects, and ad libitum energy intake (i.e. without test dish) was significantly higher under the low-fat than under the high-fat test dish condition. Thus, lean compensated 86% and obese 70% of the initial energy reduction. The cumulative fat intake (test dish included) was lower under the low-fat than under the high-fat dish condition for both weight groups. Nevertheless, the percentage of ad libitum energy intake derived from fat was significantly higher after the low-fat test dish in obese but not in lean subjects. In experiment 2, both weight groups maintained the energy and fat reduction. Thus, obese subjects did not respond differently to lean subjects to the fat and energy manipulation of the test dish, except for the percentage of fat in their diet. These results suggest that different ways of including fat-reduced foods into the habitual diet might have different effects on subsequent energy compensation.

Adult↗
PubMed1995

Seven novel mutations in the methylenetetrahydrofolate reductase gene and genotype/phenotype correlations in severe methylenetetrahydrofolate reductase deficiency.

5-Methyltetrahydrofolate, the major form of folate in plasma, is a carbon donor for the remethylation of homocysteine to methionine. This form of folate is generated from 5,10-methylenetetrahydrofolate through the action of 5,10-methylenetetrahydrofolate reductase (MTHFR), a cytosolic flavoprotein. Patients with an autosomal recessive severe deficiency of MTHFR have homocystinuria and a wide range of neurological and vascular disturbances. We have recently described the isolation of a cDNA for MTHFR and the identification of two mutations in patients with severe MTHFR deficiency. We report here the characterization of seven novel mutations in this gene: six missense mutations and a 5' splice-site defect that activates a cryptic splice site in the coding sequence. We also present a preliminary analysis of the relationship between genotype and phenotype for all nine mutations identified thus far in this gene. A nonsense mutation and two missense mutations (proline to leucine and threonine to methionine) in the homozygous state are associated with extremely low activity (0%-3%) and onset of symptoms within the 1st year of age. Other missense mutations (arginine to cysteine and arginine to glutamine) are associated with higher enzyme activity and later onset of symptoms.

Adolescent↗
PubMed1995

Gastric distension, hunger and energy intake after balloon implantation in severe obesity.

OBJECTIVE: To investigate the interrelationships between satiety feelings, abdominal perception, energy intake and weight loss, related to the presence of an intragastric balloon. DESIGN: Randomized double blind study. SUBJECTS: 20 severely obese subjects, BMI > 40 kg/m2, randomly assigned either to receive an air filled balloon (n = 11) or to have a sham procedure (n = 9). All subjects had dietary counselling to help them follow a relatively low energy diet (60% of individual spontaneous intake). MEASUREMENTS: During biweekly visits, body weight was recorded, visual analogic scales for stomach distension, hunger and feeling of balloon presence were completed. Blood chemistry profiles were monitored once every 4 weeks. RESULTS: In the balloon group, the sensations related to the presence of the balloon and to abdominal distension dramatically increased after insertion, and plateaued during the next 4 weeks. Both feelings of presence and distension decreased thereafter, and after 10 weeks they were not significantly different from those of the sham balloon group. Hunger dramatically decreased to about 30% of initial rating in the first week, but slowly returned to the initial value by the 12th week. Hunger feelings were highly and negatively correlated with feelings of distension. During the same period, the sham balloon group continued to maintain the low energy intake, and did not register any feelings of distension or presence; hunger level did not differ from initial levels throughout the whole study. The energy intake and the rate of weight loss (8-9 kg) was similar in the two groups during the study, and were not correlated with the feelings of distension. CONCLUSION: This study showed that in severely obese subjects submitted to a restrictive diet, an intragastric balloon has a measurable but transient effect on the sensation of epigastric distension and is able to decrease feelings of hunger. Unfortunately, these effects were not associated with a lower energy intake or a higher rate of weight loss than the sham situation. Thus, the present study does not support the interest of such a balloon (500 ml, air filled) in the treatment of severe obesity.

Adult↗
PubMed1994

Isolation and expression of a cDNA encoding the precursor for a novel member (ACADSB) of the acyl-CoA dehydrogenase gene family.

The acyl-CoA dehydrogenases (ACDs) are a family of mitochondrial enzymes that oxidize straight chain or branched chain acyl-CoAs in the metabolism of fatty acids or branched chain amino acids. Deficiencies in members of this gene family are important causes of human disease. A cDNA encoding the human precursor for a novel member (gene symbol ACADSB) of the ACD gene family has been isolated and characterized. The open reading frame of 1.3 kb encodes a precursor protein of 431 amino acids, which is processed in vitro to yield a mature protein of 399 amino acids. The cDNA has significant sequence similarity to other members of the acyl-CoA dehydrogenase family, with the greatest homology (38%) to the short chain acyl-CoA dehydrogenase. The cDNA was expressed in eukaryotic (COS) and prokaryotic (Escherichia coli) cells, producing a protein of the expected size, with activity toward the short branched chain acyl-CoA derivatives ((S)-2-methylbutyryl-CoA, isobutyryl-CoA, and 2-methylhexanoyl-CoA), as well as toward the short straight chain acyl-CoAs (butyryl-CoA and hexanoyl-CoA).

Acyl-CoA Dehydrogenase↗
PubMed1994

Evidence for different clinical subtypes of type 1 diabetes mellitus: a prospective study.

The purpose of this study was to determine whether the sex, age, severity of clinical presentation, presence of ICAs, IAs, and HLA-DR and DQ types could predict, in a cohort of newly-diagnosed diabetic children: (1) the duration of beta-cell function as measured by C-peptide response to a Sustacal meal; and (2) determine if those predictors could identify disease subtypes. A cohort of 170 consecutive patients was followed for 60 months after diagnosis. We found that age (0.0029), sex (0.0136), ICA (0.0001), presence of DKA (0.0070) and C-peptide peak at diagnosis (0.0000) significantly predicted the duration of residual beta-cell function over time. Furthermore, C-peptide secretion at diagnosis, presence of ICA, age and sex allowed the identification of three different prognostic groups with varying acceleration of beta-cell loss.

Adolescent↗
PubMed1994

Human methylenetetrahydrofolate reductase: isolation of cDNA, mapping and mutation identification.

Methylenetetrahydrofolate reductase (MTHFR) catalyses the reduction of methylenetetrahydrofolate to methyltetrahydrofolate, a cofactor for homocysteine methylation to methionine. MTHFR deficiency, an autosomal recessive disorder, results in homocysteinemia. Using degenerate oligonucleotides based on porcine peptide sequence data, we isolated a 90-bp cDNA by PCR from pig liver RNA. This cDNA was used to isolate a human cDNA, the predicted amino acid sequence of which shows strong homology to porcine MTHFR and to bacterial metF genes. The human gene has been localized to chromosome 1p36.3. Two mutations were identified in MTHFR-deficient patients: a missense mutation (Arg to Gln), in a residue conserved in bacterial enzymes, and a nonsense mutation (Arg to Ter).

Amino Acid Sequence↗
PubMed1994

Effects of cycles of food restriction followed by ad libitum refeeding on body composition and energy expenditure in obese rats.

Male Wistar rats rendered obese by a cafeteria diet were subjected to three successive cycles alternating food restriction with ad libitum cafeteria-diet feeding (WC rats). Body composition, energy intake, energy required for maintenance, and oxygen consumption were studied. Results were compared with those for rats fed a standard stock diet (CON rats) or a cafeteria diet (CAF rats). The rate of weight loss or regain was independent of the number of cycles. WC rats were fatter than CON rats and as fat as CAF rats after the third cycle. Cost of maintenance of WC rats decreased; their oxygen consumption decreased in the lean state, increased again in the fat state, but remained lower than that of CON and CAF rats. We conclude that the practice of successive restriction and refeeding did not result in resistance to weight loss, but rather in a defect in the utilization of energy intake, facilitating the development of obesity.

Animals↗
PubMed1994

Mutation profiles of phenylketonuria in Quebec populations: evidence of stratification and novel mutations.

Independent phenylketonuria (PKU) chromosomes (n = 109) representing 80% of a proband cohort in Quebec province carry 18 different identified mutations in 20 different mutation/haplotype combinations. The study reported here, the third in a series on Quebec populations, was done in the Montreal region and predominantly on French Canadians. It has identified three novel mutations (A309D, D338Y, and 1054/1055delG[352fs]) and one unusual mutation/RFLP haplotype combination (E280K on Hp 2). The relative frequencies and distribution of PKU mutations were then compared in three regions and population subsets (eastern Quebec, French Canadian; western Quebec, French Canadian; and Montreal, non-French Canadian). The distributions of the prevalent and rare mutations are nonrandom and provide evidence for genetic stratification. The latter and the presence of eight unusual mutation/haplotype combinations in Quebec families with European ancestries (the aforementioned four and M1V, I65T, S349P, and R408W on Hp 1) corroborate demographic and anthropologic evidence, from elsewhere, for different origins of French Canadians in eastern and western Quebec.

DNA Mutational Analysis↗